Syrian activists said Islamic State militants have beheaded women in Syria for the first time.

The Britain-based Syrian Observatory for Human Rights said Tuesday that the women were beheaded along with their husbands in Syria's eastern Deir Ezzor province after being accused of sorcery.

The Observatory, which monitors violence in Syria through a network of local sources, said the Islamic State group has executed more than 3,000 people in Syria since declaring its so-called caliphate a year ago, including nearly 1,800 civilians.

Beheadings as a means of execution are not new for the group, which has carried out multiple beheadings of Syrians as well as journalists and aid workers, including those from the United States, Britain and Japan.

Rick Brennan, RAND Corporation senior political scientist, told VOA the killings of Americans are what has spurred U.S. officials to take action against the militants.

Motivated to act

"That's the only thing that has motivated the United States to act so far, it has been the beheading of the Americans, when the British citizens were killed, those types of situations is what's causing motivation because it stirs public support within those countries," Brennan said.

"But if you're looking at a more large-scale response, it will take some sort of horrific event that occurs in some Western country that will trigger the type of public reaction where public officials have to respond," he added.

James Jeffrey, a former U.S. ambassador and now a regional analyst at the Washington Institute on Near East Policy, told VOA that the U.S.-led coalition campaign has done little to counter the Islamic State group.

"They're barely contained. They haven't been seriously degraded. They've been able to replace many of their losses and they certainly haven't been destroyed," Jeffrey said.

He also said that right now the Islamic State group is "no doubt" the biggest terror threat in the world.

"It's a whole dimension bigger than al-Qaida ever was," Jeffrey said. "It can take down countries. Al-Qaida never had that ability."